Described herein are imaging members, and more specifically, multi-layered photoconductive imaging members comprised of a substrate, an optional conductive layer, an optional undercoat layer, an optional adhesive layer, a charge generating layer, a charge transport layer, and an optional overcoat layer.
Layered photoconductive imaging members have been described in numerous U.S. patents, such as U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference, wherein there is illustrated an imaging member comprised of a charge generating layer, and an aryl amine hole transport layer. Examples of charge generating layer components include trigonal selenium, metal phthalocyanines, vanadyl phthalocyanines, and metal free phthalocyanines. Additionally, there is described in U.S. Pat. No. 3,121,006, the disclosure of which is totally incorporated herein by reference, a composite xerographic photoconductive member comprised of finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder.
In U.S. Pat. No. 4,587,189, the disclosure of which is totally incorporated herein by reference, there is illustrated a layered imaging member with, for example a perylene, pigment charge generating component. Other components, such as the charge generating compounds and the aryl amine charge transport material, can be selected for the imaging members in various embodiments.
In U.S. Pat. No. 4,921,769, the disclosure of which is totally incorporated herein by reference, there are illustrated photoconductive imaging members with blocking layers of certain polyurethanes.
Illustrated in U.S. Pat. Nos. 6,255,027; 6,177,219, and 6,156,468, the disclosures of which are totally incorporated herein by reference, are, for example, photoreceptors containing a hole blocking layer of a plurality of light scattering particles dispersed in a binder, reference for example, Example I of U.S. Pat. No. 6,156,468, the disclosure of which is totally incorporated herein by reference, wherein there is illustrated a hole blocking layer of titanium dioxide dispersed in a specific linear phenolic binder of VARCUM®, available from OxyChem Company.
Sensitivity is a very important electrical characteristic of photoconductive imaging members or photoreceptors. Sensitivity may be described in two aspects. The first aspect of sensitivity is spectral sensitivity, which refers to sensitivity as a function of wavelength. An increase in spectral sensitivity implies an appearance of sensitivity at a wavelength in which previously no sensitivity was detected. The second aspect of sensitivity, broadband sensitivity, is a change of sensitivity (e.g., an increase) at a particular wavelength previously exhibiting sensitivity, or a general increase of sensitivity encompassing all wavelengths previously exhibiting sensitivity. This second aspect of sensitivity may also be described as change of sensitivity, encompassing all wavelengths, with a broadband (white) light exposure. A common problem encountered in the manufacturing of photoreceptors is maintaining consistent spectral and broadband sensitivity from batch to batch.
To satisfy these demands, photoreceptors with different charge generating layer formulations providing varying photosensitivities may be utilized. Charge generating layers are often formed by layering a dispersion of photoconductive pigments on to the photoreceptor. The cost to develop different photoconductive pigments and different charge generating layer coating dispersion formulations and to change dispersion solutions for different products in the manufacturing process greatly increases the costs to manufacture photoreceptors.
Thus, it is desirable that the electrical characteristics of photoreceptors be consistent during the manufacturing process, while keeping the cost of manufacture low. Further, it is desirable to permit printing with a minimum number of photoconductive passes.